Patent Application
20090193797
1. Field of the Invention
This invention relates to a device and method using infrared to enhance selective catalytic reduction (SCR) of NOx, consisting of at least an infrared-emitting body, said infrared-emitting body being engineered to have specific spectral luminance covering a part or the whole of 3-14 μm wavelength range, that provides an effective means for improving NOx conversion in the SCR aftertreatment system of diesel engines.
2. Description of Prior Art
The combustion of fossil fuel always leads to the formation of nitrogen oxides (NOx). NOx formation mechanisms in internal combustion engines are well known and details published in textbooks. The term “NOx” is used primarily to describe two species: nitric oxide (NO) and nitrogen oxide (NO2). Sometimes the term is extended to include other oxides such as a nitrous oxide (NO2), which is insignificant and often ignored.
The most desirable removal mechanism would be direct decomposition of NOx. The selective catalytic reduction (SCR) is a validated technology for the removal of NOx in diesel exhaust. There are commercial exhaust aftertreatment systems that employ intentional injection of some reducing agent into the exhaust gas. This is called “active deNOx”. The reducing agent is usually ammonia or urea, while some researchers are pursuing methods using hydrocarbons as reducing agent.
The strategy of urea-SCR is to set free NH3 from urea, CO(NH2)2, by thermolysis and hydrolysis as given in the chemical equation (1):
CO(NH2)2→HNCO+NH3. . . (by thermolysis)
HNCO→NH3+CO2. . . (by hydrolysis) (1)
The NH3 radical then reacts with NO and NO2 as depicted in chemical equations (2) and (3):
6NO+4NH3→5N2+6H2O (2)
6NO2+8NH3→7N2+12H2O (3)
An undesired byproduct, such as biuret (NH2CONHCONH2), can be produced if urea solution is not properly thermolyzed or hydrolyzed.
An alternative method is the use of a light hydrocarbon, such as propylene, propane, or methane as a reluctant during the selective catalytic reduction of NOx (HC—SCR). As such, hydrocarbons can be provided from the fuel source, thus adding no new storage, transportation or corrosion concerns. For example, the propylene C3H6 reacts with NO in the way as described in chemical equation (4)
2C3H6+18NO→9N2+6H2O+6CO2 (4)
The present inventor had realized the scientific fact that hydrocarbons are “infrared-active” and absorb infrared photons shorter than 20 μm in wavelengths causing vibrations, which resulted in the inventions of fuel combustion enhancement devices as described in U.S. Pat. Nos. 6,026,788 and 6,082,339 (by the present inventor). Quantum Mechanically speaking, infrared-excited hydrocarbon molecules have lower activation barriers and thus get higher chemical reaction rates. The present inventor had developed several infrared-emitting bodies in 3-14 μm wavelengths, which are categorized as “mid-infrared” in NASA definition but “far-infrared” in Japanese convention. The present inventor was able to use the IR-emitters to validate underlying science of infrared-excitation in Methane-Air Counterflow Flame experiments. Infrared was found helping improve 6 % combustion efficiency in combustion of methane-air mixture as described in reaction (5).
CH4+O2→CO+H2+H2O
furthermore H2+½O2→H2O
CO+½O2→CO2 (5)
In real diesel engine applications, the present inventor discovered experimentally that such IR-emitters could also enhance the reduction reaction described in equation (4) for removal of NOx. Through literature search, the present inventor further realized that the bonds in urea and ammonia molecules, including N—H, —NH2, —CONH—, and —CONH2, also absorb infrared in 3-14 μm wavelengths to cause molecular excitations. In other words, urea and ammonia are so-called “infrared-active”.
For example, —HNCO—bond vibrates at 3.23-3.26 and 6.45-6.62 μm bands, while the —NH2 bonds absorb photons at 3.029 μm, 3.106 μm, and 6.680 μm wavelengths to respectively cause symmetric, asymmetric, and bending vibrations. The vibrational modes also include overtones at bands 4.52-4.72, 6.58-6.76, 9.57-9.85, 11.90-12.50, and 12.20-12.99 μm, which all fall in said 3-14 μm wavelength range. It became evident that infrared can help enhancing urea-SCR reaction in equations (1), (2), and (3), and HC—SCR in equation (4), because all reactants in the equation are all infrared-active. Besides, the bonds of biuret (NH2CONHCONH2) are found to vibrate at 4.72-4.93 and 6.80-6.92 μm bands so that infrared excitation may raise reduction of biuret and limit its production in the processes.
As previously mentioned, the present inventor had discovered the use of infrared in 3-14 μm wavelengths for improving combustion efficiency of hydrocarbon fuel in internal combustion engines as disclosed in U.S. Pat. Nos. 6,026,788 and 6,082,339 by the present inventor. Since then, a number of similar inventions had followed, for examples U.S. Pat. Nos. 7,021,297, 7,036,492, and 7,281,526, just to name a few. Even so, the prior arts only described the use of infrareds in oxidation of hydrocarbons and failed to teach the use of infrareds for aiding selective catalytic reduction (SCR) of NOx using urea, ammonia, and hydrocarbons as reducing agents in diesel applications.
Accordingly, one object of this invention is to provide a device and method that can increase the efficiency of a selective catalytic reduction (SCR) of NOx aftertreatment using urea, ammonia, hydrocarbons, or other infrared-active substances as reducing agent(s).
Another object of the present invention is to provide a simple, easy-to-implement, and maintenance-free infrared-enhanced SCR of NOx device.
These objectives are achieved by an infrared-enhanced SCR device comprising essentially at least one infrared emitting body having specific spectral luminance covering a part or whole of 3-14 μm wavelength range. The device can be disposed in the delivery system of reducing agent for said SCR system to excite the reluctant before it mixes with exhausts gas for reduction of NOx.
Other objects, features and advantages of the present invention will hereinafter become apparent to those skilled in the art from the following description.
In accordance with the present invention an infrared-enhanced selective catalytic reduction (SCR) of NOx aftertreatment device and method consists of at least an infrared emitting body having specific spectral luminance covering a part or the whole of 3-14 μm wavelength range. It can enhance NOx conversion efficiency of said SCR system, resulting in reduced NOx in exhaust. The infrared emitting body can be disposed in the passageway of reducing agent for said SCR aftertreatment to energize the reluctant before it mixes with exhaust gas for NOx reduction.
It is well known that absorption of an infrared photon at a wavelength shorter than 20 μm (micrometer) gives rise to bond stretching or bending vibration in molecules that are “infrared-active”. In fact, Organic Chemists have been using IR absorption spectral analysis (so-called “Infrared Correlation Charts”) to identify unknown specimens for decades. Based on spectral absorption profiles in 3-7 μm (so-called “Functional Group” zone) and 7-20 μm (“Signature” zone) the test specimen can be precisely identified. However, what people had long ignored was absorbing IR photons can increase kinetic energy of covalent bonds and thus cause molecule to vibrate. It not only changes dipole moment of the molecule, but also decreases activation barrier of the bond and thus increases reaction chemical rate, which is described in equation (6) by Quantum Mechanics:
Reaction Rate: W=Ke−E/RT (6)
where K is a constant, E activation energy, and T temperature (in Kelvin). Equation (6) predicts an increased reaction rate W with a reduced activation energy E.
The present inventor had reported favorable results on using the devices as described in U.S. Pat. No. 6,026,788 to excite fuels for enhanced engine performance. The net results were improved fuel combustion efficiency with increased torque/power, reduced fuel consumption, and lowered emissions. In real diesel engine applications the present inventor recognized that the reducing agents such as urea, ammonia, or hydrocarbons used in commercial urea-SCR or HC—SCR aftertreatment systems for removal of NOx are all “infrared-active”. In urea and ammonia, bonds such as N—H, —NH2, and primary and secondary amide —CONH2 show strong absorption for combination and overtone modes in 3-7 μm wavelengths (i.e. Zone I). There are other overtone bands in long wavelengths, but often too weak to be noticed.
The present inventor learned from Japanese published results and experimentally confirmed that adding cobalt oxide and/or nickel oxides to the oxide mixture as disclosed in U.S. Pat. No. 6,026,788 can boost the radiation strength at short wavelengths. Meanwhile, increasing ceramic processing temperature from a conventional 1200° C. to above 1350° C. can further strengthen spectral luminance of the resultant IR-emitter at short wavelengths. Accordingly, several examples of the present invention were prepared for demonstration.
In other embodiments the infrared emitting bodies can be disposed in the interior of a supply line or nozzle assembly by embedding or coating on the inner wall, or being a part of the reducing agent delivery system.
Several demonstration samples were made with 40 (weight) % silicate, 25% alumina, 17% zirconia, 7% magnesium oxide, 5% cobalt oxide, and other minor elements and processed at a temperature above 1350° C. An SEM/EDS (scanning electron microscope with energy dispersive spectrometry) plot was run with the samples to obtain a quantitative analysis on the elemental composition of the oxide compounds. In lab, an infrared imaging camera with variable wavelength band filters was used to determine the spectral luminance for these IR-emitters. The IR-emitter was tested by mounting it on a Teflon fuel hose to an HC—SCR system with a zeolites catalyst. The preliminary test result seemed very encouraging, while further scientific investigation remained to be done.
According to the present invention, an infrared-enhanced selective catalytic reduction (SCR) device comprises at least an infrared emitting body having specific spectral luminance covering a part or the whole of 3-14 μm wavelength range, which can be disposed in the passageway of the reducing-agent to said SCR system for better NOx conversion.
The invention has been described above. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. Such variations are not to be regarded as a departure from the spirit and scope of the invention and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
